Model

Getting Started

To include the source files for Model and its dependencies, first load the YUI seed file if you haven't already loaded it.

<script src="http://yui.yahooapis.com/3.4.0/build/yui/yui-min.js"></script>

Next, create a new YUI instance for your application and populate it with the modules you need by specifying them as arguments to the YUI().use() method. YUI will automatically load any dependencies required by the modules you specify.

// Create a new YUI instance and populate it with the required modules.
YUI().use('model', function (Y) {
    // Model is available and ready for use. Add implementation
    // code here.
});

For more information on creating YUI instances and on the use() method, see the documentation for the YUI Global object.

What is a Model?

A model is a class that manages data, state, and behavior associated with an application or a part of an application.

For example, in a photo gallery, you might use a model to represent each photo. The model would contain information about the image file, a caption, tags, etc., along with methods for working with this data. The model would also be responsible for validating any new data before accepting it.

While Model may be used as a standalone component, it's common to associate a Model instance with a View instance, which is responsible for rendering the visual representation of the data contained in the model and updating that representation when the model changes.

Using Model

Extending Y.Model

The first step in creating a custom Model class is to extend Y.Model. This allows you to define the data attributes your Model class will manage, as well as helper methods, validators, and (optionally) a sync layer for your Model class.

In this example, we'll create a Y.PieModel class. Each instance of this class will represent a delicious pie, fresh from the oven.

// Create a new Y.PieModel class that extends Y.Model.
Y.PieModel = Y.Base.create('pieModel', Y.Model, [], {
  // Add prototype methods for your Model here if desired. These methods will be
  // available to all instances of your Model.

  // Returns true if all the slices of the pie have been eaten.
  allGone: function () {
    return this.get('slices') === 0;
  },

  // Consumes a slice of pie, or fires an `error` event if there are no slices
  // left.
  eatSlice: function () {
    if (this.allGone()) {
      this.fire('error', {
        type : 'eat',
        error: "Oh snap! There isn't any pie left."
      });
    } else {
      this.set('slices', this.get('slices') - 1);
      Y.log('You just ate a slice of delicious ' + this.get('type') + ' pie!');
    }
  }
}, {
  ATTRS: {
    // Add custom model attributes here. These attributes will contain your
    // model's data. See the docs for Y.Attribute to learn more about defining
    // attributes.

    slices: {
      value: 6 // default value
    },

    type: {
      value: 'apple'
    }
  }
});

Now we can create instances of Y.PieModel to represent delicious pies.

Each instance will have a type attribute containing the type of the pie and a slices attribute containing the number of slices remaining. We can call the allGone() method to check whether there are any slices left, and the eatSlice() method to eat a slice.

// Bake a delicious new pecan pie.
var pecanPie = new Y.PieModel({type: 'pecan'});

pecanPie.on('error', function (e) {
  Y.log(e.error);
});

pecanPie.eatSlice(); // => "You just ate a slice of delicious pecan pie!"
Y.log(pecanPie.get('slices')); // => 5

Five slices later, our pie will be all gone. If we try to eat another slice, we'll get an error event.

// 5 slices later...
pecanPie.eatSlice(); // => "Oh snap! There isn't any pie left."

Model Attributes

A Model's data is represented by attributes. The Model class provides two built-in attributes, clientId and id. The rest are up to you to define when you extend Y.Model.

Built-in Attributes

Attribute	Default Value	Description
clientId	generated id	An automatically generated client-side only unique ID for identifying model instances that don't yet have an id. The client id is guaranteed to be unique among all models on the current page, but is not unique across pageviews. Client ids are never included in toJSON() output.
id	null	A globally unique identifier for the model instance. If this is null, then the model instance is assumed to be "new" (meaning it hasn't yet been saved to a persistence layer). If the model represents data that's stored in a database of some kind, it usually makes sense to use the database's primary key here. If your persistence layer uses a primary key with a name other than id, you can override the idAttribute property and set it to the name of your custom id attribute when extending Y.Model (be sure to define a corresponding attribute as well). The id attribute will then act as an alias for your custom id attribute.

Custom Attributes

Custom attributes are where all your model's data should live. You define these attributes when you first extend Y.Model. You can set their values by passing a config object into the model's constructor, or by calling the model's set() or setAttrs() methods..

Attributes can specify default values, getters and setters, validators, and more. For details, see the documentation for the Attribute component.

Model Properties

The following properties are available on Model instances. The idAttribute property may be overridden when extending Y.Model; the others are intended to be read-only.

Property	Type	Description
changed	Object	Hash of attributes that have changed since the last time the model was saved.
idAttribute	String	Name of the attribute to use as the unique id for the model. Defaults to "id", but you may override this property when extending Y.Model if you want to specify a custom id attribute.
lastChange	Object	Hash of attributes that were changed in the most recent change event. Each item in this hash is an object with the following properties: newVal The new value of the attribute after it changed. prevVal The old value of the attribute before it changed. src The source of the change, or null if no source was specified when the change was made. This can be set to any string you want by passing an options object like {src: 'foo'} to the set() or setAttrs() methods when changing attribute values. Its purpose is to allow you to identify the source of the change later by inspecting the src property associated with an event, so choose a string that has meaning for your particular use case.
lists	Array	Array of ModelList instances that contain this model. This property is updated automatically when the model is added to or removed from a ModelList instance. You shouldn't alter it manually. When working with models in a list, you should always add and remove models using the list's add() and remove() methods.

Model Events

Model instances provide the following events:

Event	When	Payload
change	One or more attributes on the model are changed.	changed (Object) Hash of change information for each attribute that changed. Keys are attribute names, values are objects with the following properties: newVal The new value of the attribute after it changed. prevVal The old value of the attribute before it changed. src The source of the change, or null if no source was specified when the change was made. This can be set to any string you want by passing an options object like {src: 'foo'} to the set() or setAttrs() methods when changing attribute values. Its purpose is to allow you to identify the source of the change later by inspecting the src property associated with an event, so choose a string that has meaning for your particular use case.
error	An error occurs, such as when the model fails validation or a sync layer response can't be parsed.	error Error message, object, or exception generated by the error. Calling toString() on this should result in a meaningful error message. src Source of the error. May be one of the following default sources, or any custom error source used by your Model subclass): parse An error parsing a response from a sync layer. validate The model failed to validate.

A model's events bubble up to any model lists that the model belongs to. This enables you to use the model list as a central point for handling model value changes and errors.

Change Events

In addition to the master change event, which is fired whenever one or more attributes are changed, there are also change events for each individual attribute.

Attribute-level change events follow the naming scheme nameChange, where name is the name of an attribute.

// Bake a new pie model.
var pie = new Y.PieModel();

// Listen for all attribute changes.
pie.on('change', function (e) {
  Y.log('change fired: ' + Y.Object.keys(e.changed).join(', '));
});

// Listen for changes to the `slices` attribute.
pie.on('slicesChange', function (e) {
  Y.log('slicesChange fired');
});

// Listen for changes to the `type` attribute.
pie.on('typeChange', function (e) {
  Y.log('typeChange fired');
});

// Change multiple attributes at once.
pie.setAttrs({
  slices: 3,
  type  : 'maple custard'
});

// => "slicesChange fired"
// => "typeChange fired"
// => "change fired: slices, type"

Firing Your Own Error Events

In your custom model class, there may be situations beyond just parsing and validating in which an error event would be useful. For example, in the Y.PieModel class, we fire an error when someone tries to eat a slice of pie and there are no slices left.

// Consumes a slice of pie, or fires an `error` event if there are no slices
// left.
eatSlice: function () {
  if (this.allGone()) {
    this.fire('error', {
      type : 'eat',
      error: "Oh snap! There isn't any pie left."
    });
  } else {
    this.set('slices', this.get('slices') - 1);
    Y.log('You just ate a slice of delicious ' + this.get('type') + ' pie!');
  }
}

When firing an error event, set the type property to something that users of your class can use to identify the type of error that has occurred. In the example above, we set it to "eat", because it occurred when the caller tried to eat a slice of pie.

The error property should be set to an error message, an Error object, or anything else that provides information about the error and has a toString() method that returns an error message string.

Working with Model Data

Getting and Setting Attribute Values

Model's get() and set() methods are the main ways of interacting with model attributes. Unsurprisingly, they allow you to get and set the value of a single attribute.

var pie = new Y.PieModel();

// Set the value of the `type` attribute.
pie.set('type', 'banana cream');

// Get the value of the `type` attribute.
pie.get('type'); // => "banana cream"

Model also provides two convenience methods for getting and escaping an attribute value in a single step. The getAsHTML() method returns an HTML-escaped value, and the getAsURL() method returns a URL-encoded value.

pie.set('type', 'strawberries & cream');

pie.getAsHTML('type'); // => "strawberries & cream"
pie.getAsURL('type');  // => "strawberries%20%26%20cream"

The getAttrs() and setAttrs() methods may be used to get and set multiple attributes at once. getAttrs() returns a hash of all attribute values, while setAttrs() accepts a hash of attribute values. When you set multiple attributes with setAttrs(), it fires only a single change event that contains all the affected attributes..

pie.setAttrs({
  slices: 6,
  type  : 'marionberry'
});

pie.getAttrs();
// => {
//   clientId: "pieModel_1",
//   destroyed: false,
//   id: null,
//   initialized: true,
//   slices: 6,
//   type: "marionberry"
// }

The destroyed and initialized attributes you see in the sample output above are lifecycle attributes provided by Y.Base, and aren't actually model data.

To get a slightly more useful representation of model data, use the toJSON() method. The toJSON() method excludes the clientId, destroyed, and initialized attributes, making the resulting object more suitable for serialization and for storing in a persistence layer.

pie.toJSON();
// => {
//   id: null,
//   slices: 6,
//   type: "marionberry"
// }

If a custom idAttribute is in use, the toJSON() output will include that id attribute instead of id.

// toJSON() output with a custom id attribute.
pie.toJSON();
// => {
//   customId: null,
//   slices: 6,
//   type: "marionberry"
// }

If you'd like to customize the serialized representation of your models, you may override the toJSON() method.

When using the set() and setAttrs() methods, you may pass an optional options argument. If options.silent is true, no change event will be fired.

// Set attributes without firing a `change` event.
pie.set('slices', 0, {silent: true});

pie.setAttrs({
  slices: 0,
  type  : 'chocolate cream'
}, {silent: true});

After making changes to a model's attributes, you may call the undo() method to undo the previous change.

var pie = new Y.PieModel({slices: 6});

pie.set('slices', 5);
pie.undo();
pie.get('slices'); // => 6

Note that there's only a single level of undo, so it's not possible to revert past the most recent change.

Validating Changes

Validating model changes as they occur is a good way to ensure that the data in your models isn't nonsense, especially when dealing with user input.

There are two ways to validate model attributes. One way is to define an attribute validator function for an individual attribute when you extend Y.Model.

// Defining an individual attribute validator.
Y.PieModel = Y.Base.create('pieModel', Y.Model, [], {
  // ... prototype methods and properties ...
}, {
  ATTRS: {
    slices: {
      value: 6,
      validator: function (value) {
        return typeof value === 'number' && value >= 0 && value <= 10;
      }
    },

    // ...
  }
});

For more details on attribute validators, see the Attribute User Guide.

The second way to validate changes is to provide a custom validate() method when extending Y.Model. When one or more model attributes are changed, this method will receive a hash of attributes that have changed. If the validate() method returns anything other than null or undefined, it will be considered a validation failure and an error event will be fired with the returned value as the error message.

// Defining a model-wide `validator()` method.
Y.PieModel = Y.Base.create('pieModel', Y.Model, [], {
  // ... prototype methods and properties ...

  validate: function (attributes) {
    var slices;

    switch (attributes.type) {
    case 'rhubarb':
      return 'Eww. No. Not allowed.';

    case 'maple custard':
      slices = Y.Lang.isValue(attributes.slices) ?
          attributes.slices : this.get('slices');

      if (slices < 10) {
        return "Making fewer than 10 slices of maple custard pie would be " +
            "silly, because I'm just going to eat 8 of them as soon as it's " +
            "out of the oven.";
      }
    }
  }
}, {
  // ... attributes ...
});

Loading and Saving Model Data

Calling a model's load() and save() methods will result in a behind-the-scenes call to the model's sync() method specifying the appropriate action.

The default sync() method does nothing, but by overriding it and providing your own sync layer, you can make it possible to create, read, update, and delete models from a persistence layer or a server. See Implementing a Model Sync Layer for more details.

The load() and save() methods each accept two optional parameters: an options object and a callback function. If provided, the options object will be passed to the sync layer, and the callback will be called after the load or save operation is finished. You may provide neither parameter, or just an options object, or just a callback, although if you provide both an options object and a callback, they need to be in that order.

The callback function will receive two parameters: an error (this parameter will be null or undefined if the operation was successful) and a response (which is the result of calling the model's parse() method with whatever response the sync layer returned).

The load() method calls sync() with the read action, and automatically updates the model with the response data (by passing it to parse() and then updating attributes based on the hash that parse() returns) before calling the callback.

var pie = new Y.PieModel({id: 'pie123'});

// Load a pie model, passing a callback that will run when the model has
// been loaded.
pie.load(function (err, response) {
  if (!err) {
    // Success! The model now contains the loaded data.
  }
});

The save() method will do one of two things: if the model is new (meaning it doesn't yet have an id value), it will call sync() with the "create" action. If the model is not new, then it will call sync() with the "update" action.

If the sync layer returns a response, then save() will update the model's attributes with the response data before calling the callback function.

// Save a pie model, passing a callback that will run when the model has
// been saved.
pie.save(function (err, response) {
  if (!err) {
    // Success! The model has been saved. If the sync layer returned a response,
    // then the model has also been updated with any new data in the response.
  }
});

Always use the load() or save() methods rather than calling sync() directly, since this ensures that the sync layer's response is passed through the parse() method and that the model's data is updated if necessary.

The Model Lifecycle

When a model is first created and doesn't yet have an id value, it's considered "new". The isNew() method will tell you whether or not a model is new.

Once a model has an id value, either because one was manually set or because the model received one when it was loaded or saved, the model is no longer considered new, since it is assumed to exist in a persistence layer or on a server somewhere.

If a model is new or if any of its attributes have changed since the model was last loaded or saved, the model is considered "modified". The isModified() method will tell you whether or not a model is modified. A successful call to load() or save() will reset a model's "modified" flag.

Finally, a model's destroy() method can be used to destroy the model instance. Calling destroy() with no arguments will destroy only the local model instance, while calling destroy({'delete': true}) will both destroy the local model instance and call the sync layer with the "delete" action to delete the model from a persistence layer or server.

It's not necessary for a model to support all possible sync actions. A model that's used to represent read-only data might use a sync layer that only implements the read action, for instance. In this case, the other actions should simply be no-ops that either call the sync callback immediately, or pass an error to the sync callback indicating that the action isn't supported (depending on your personal preference).

Implementing a Model Sync Layer

A model's save(), load(), and destroy() methods all internally call the model's sync() method to carry out an action. The default sync() method doesn't actually do anything, but by overriding the sync() method, you can provide a custom sync layer.

A sync layer might make Ajax requests to a remote server, or it might act as a wrapper around local storage, or any number of other things.

The sync() Method

When the sync() method is called, it receives three arguments:

action (String)

A string that indicates the intended sync action. May be one of the following values:

create

Create a new model record. The "create" action occurs when a model is saved and doesn't yet have an id value.

read

Read an existing model record. The record should be identified based on the id attribute of the model.

update

Update an existing model record. The "update" action occurs when a model is saved and already has an id value. The record to be updated should be identified based on the id attribute of the model.

delete

Delete an existing model record. The record to be deleted should be identified based on the id attribute of the model.

options (Object)

A hash containing any options that were passed to the save(), load() or destroy() method. This may be used to pass custom options to a sync layer.

callback (Function)

A callback function that should be called when the sync operation is complete. The callback expects to receive the following arguments:

err

Error message or object if an error occured, null or undefined if the operation was successful.

response

Response from the persistence layer, if any. This will be passed to the parse() method to be parsed.

Implementing a sync layer is as simple as handling the requested sync action and then calling the callback function. Here's a sample sync layer that stores records in local storage (note: this example requires the json-stringify module):

Y.PieModel = Y.Base.create('pieModel', Y.Model, [], {
  // ... prototype methods and properties ...

  // Custom sync layer.
  sync: function (action, options, callback) {
    var data;

    switch (action) {
      case 'create':
        data = this.toJSON();

        // Use the current timestamp as an id just to simplify the example. In a
        // real sync layer, you'd want to generate an id that's more likely to
        // be globally unique.
        data.id = Y.Lang.now();

        // Store the new record in localStorage, then call the callback.
        localStorage.setItem(data.id, Y.JSON.stringify(data));
        callback(null, data);
        return;

      case 'read':
        // Look for an item in localStorage with this model's id.
        data = localStorage.getItem(this.get('id'));

        if (data) {
          callback(null, data);
        } else {
          callback('Model not found.');
        }

        return;

      case 'update':
        data = this.toJSON();

        // Update the record in localStorage, then call the callback.
        localStorage.setItem(this.get('id'), Y.JSON.stringify(data));
        callback(null, data);
        return;

      case 'delete':
        localStorage.removeItem(this.get('id'));
        callback();
        return;

      default:
        callback('Invalid action');
    }
  }
}, {
  // ... attributes ...
});

The parse() Method

Depending on the kind of response your sync layer returns, you may need to override the parse() method as well. The default parse() implementation knows how to parse JavaScript objects and JSON strings that can be parsed into JavaScript objects representing a hash of attributes. If your response data is in another format, such as a nested JSON response or XML, override the parse() method to provide a custom parser implementation.

If an error occurs while parsing a response, fire an error event with type "parse".

This sample demonstrates a custom parser for responses in which the model data is contained in a data property of the response object.

// Custom response parser.
parse: function (response) {
  if (response.data) {
    return response.data;
  }

  this.fire('error', {
    type : 'parse',
    error: 'No data in the response.'
  });
}